DESCRIPTION

These routines provide various interfaces to the LDAP bind operation.
After an association with an LDAP server is made using
ldap_init(3),
an LDAP bind operation should be performed before other operations are
attempted over the connection. An LDAP bind is required when using
Version 2 of the LDAP protocol; it is optional for Version 3 but is
usually needed due to security considerations.

There are three types of bind calls, ones providing simple authentication,
ones providing SASL authentication, and general routines capable of doing
either simple or SASL authentication.

SASL
(Simple Authentication and Security Layer)
that can negotiate one of many different kinds of authentication.
Both synchronous and asynchronous versions of each variant of the bind
call are provided. All routines
take ld as their first parameter, as returned from
ldap_init(3).

SIMPLE AUTHENTICATION

The simplest form of the bind call is
ldap_simple_bind_s().
It takes the DN to bind as in who, and the userPassword associated
with the entry in passwd. It returns an LDAP error indication
(see
ldap_error(3)).
The
ldap_simple_bind()
call is asynchronous,
taking the same parameters but only initiating the bind operation and
returning the message id of the request it sent. The result of the
operation can be obtained by a subsequent call to
ldap_result(3).

GENERAL AUTHENTICATION

The
ldap_bind()
and
ldap_bind_s()
routines can be used when the
authentication method to use needs to be selected at runtime. They
both take an extra method parameter selecting the authentication
method to use. It should be set to LDAP_AUTH_SIMPLE
to select simple authentication.
ldap_bind()
returns the message id of the request it initiates.
ldap_bind_s()
returns an LDAP error indication.

SASL AUTHENTICATION

For SASL binds the server always ignores any provided DN, so the
dn
parameter should always be NULL.
ldap_sasl_bind_s()
sends a single SASL bind request with the given SASL
mechanism
and credentials in the
cred
parameter. The format of the credentials depends on the particular
SASL mechanism in use. For mechanisms that provide mutual authentication
the server's credentials will be returned in the
servercredp
parameter.
The routine returns an LDAP error indication (see
ldap_error(3)).
The
ldap_sasl_bind()
call is asynchronous, taking the same parameters but only sending the
request and returning the message id of the request it sent. The result of
the operation can be obtained by a subsequent
call to
ldap_result(3).
The result must be additionally parsed by
ldap_parse_sasl_bind_result()
to obtain any server credentials sent from the server.

Many SASL mechanisms require multiple message exchanges to perform a
complete authentication. Applications should generally use
ldap_sasl_interactive_bind_s()
rather than calling the basic
ldap_sasl_bind()
functions directly. The
mechs
parameter should contain a space-separated list of candidate mechanisms
to use. If this parameter is NULL or empty the library will query
the supportedSASLMechanisms attribute from the server's rootDSE
for the list of SASL mechanisms the server supports. The
flags
parameter controls the interaction used to retrieve any necessary
SASL authentication parameters and should be one of:

LDAP_SASL_AUTOMATIC

use defaults if available, prompt otherwise

LDAP_SASL_INTERACTIVE

always prompt

LDAP_SASL_QUIET

never prompt

The
interact
function uses the provided
defaults
to handle requests from the SASL library for particular authentication
parameters. There is no defined format for the
defaults
information;
it is up to the caller to use whatever format is appropriate for the
supplied
interact
function.
The
sasl_interact
parameter comes from the underlying SASL library. When used with Cyrus SASL
this is an array of
sasl_interact_t
structures. The Cyrus SASL library will prompt for a variety of inputs,
including:

SASL_CB_GETREALM

the realm for the authentication attempt

SASL_CB_AUTHNAME

the username to authenticate

SASL_CB_PASS

the password for the provided username

SASL_CB_USER

the username to use for proxy authorization

SASL_CB_NOECHOPROMPT

generic prompt for input with input echoing disabled

SASL_CB_ECHOPROMPT

generic prompt for input with input echoing enabled

SASL_CB_LIST_END

indicates the end of the array of prompts

See the Cyrus SASL documentation for more details.

REBINDING

The
ldap_set_rebind_proc
function() sets the process to use for binding when an operation returns a
referral. This function is used when an application needs to bind to another server
in order to follow a referral or search continuation reference.

The function takes ld, the rebind function, and the params,
the arbitrary data like state information which the client might need to properly rebind.
The LDAP_OPT_REFERRALS option in the ld must be set to ON for the libraries
to use the rebind function. Use the
ldap_set_option
function to set the value.

The rebind function parameters are as follows:

The ld parameter must be used by the application when binding to the
referred server if the application wants the libraries to follow the referral.

The url parameter points to the URL referral string received from the LDAP server.
The LDAP application can use the
ldap_url_parse(3)
function to parse the string into its components.

The request parameter specifies the type of request that generated the referral.

The msgid parameter specifies the message ID of the request generating the referral.

The params parameter is the same value as passed originally to the
ldap_set_rebind_proc()
function.

The LDAP libraries set all the parameters when they call the rebind function. The application
should not attempt to free either the ld or the url structures in the rebind function.

The application must supply to the rebind function the required authentication information such as,
user name, password, and certificates. The rebind function must use a synchronous bind method.

UNBINDING

The
ldap_unbind()
call is used to unbind from the directory,
terminate the current association, and free the resources contained
in the ld structure. Once it is called, the connection to
the LDAP server is closed, and the ld structure is invalid.
The
ldap_unbind_s()
call is just another name for
ldap_unbind();
both of these calls are synchronous in nature.

The
ldap_unbind_ext()
and
ldap_unbind_ext_s()
allows the operations to specify controls.

ERRORS

Asynchronous routines will return -1 in case of error, setting the
ld_errno parameter of the ld structure. Synchronous
routines return whatever ld_errno is set to. See
ldap_error(3)
for more information.

NOTES

If an anonymous bind is sufficient for the application, the rebind process
need not be provided. The LDAP libraries with the LDAP_OPT_REFERRALS option
set to ON (default value) will automatically follow referrals using an anonymous bind.

If the application needs stronger authentication than an anonymous bind,
you need to provide a rebind process for that authentication method.
The bind method must be synchronous.